Effect of Endotracheal Tube Size, Respiratory System Mechanics, and Ventilator Settings on Driving Pressure.

OBJECTIVES: We sought to investigate factors that affect the difference between the peak inspiratory pressure measured at the Y-piece under dynamic flow conditions and plateau pressure measured under zero-flow conditions (resistive pressure) during pressure controlled ventilation across a range of endotracheal tube sizes, respiratory mechanics, and ventilator settings. DESIGN: In vitro study. SETTING: Research laboratory. PATIENTS: None. INTERVENTIONS: An in vitro bench model of the intubated respiratory system during pressure controlled ventilation was used to obtain the difference between peak inspiratory pressure measured at the Y-piece under dynamic flow conditions and plateau pressure measured under zero-flow conditions across a range of endotracheal tubes sizes (3.0-8.0 mm). Measurements were taken at combinations of pressure above positive end-expiratory pressure (10, 15, and 20 cm H2O), airway resistance (no, low, high), respiratory system compliance (ranging from normal to extremely severe), and inspiratory time at constant positive end-expiratory pressure (5 cm H2O). Multiple regression analysis was used to construct models predicting resistive pressure stratified by endotracheal tube size. MEASUREMENTS AND MAIN RESULTS: On univariate regression analysis, respiratory system compliance (ß -1.5; 95% CI, -1.7 to -1.4; p < 0.001), respiratory system resistance (ß 1.7; 95% CI, 1.5-2.0; p < 0.001), pressure above positive end-expiratory pressure (ß 1.7; 95% CI, 1.4-2.0; p < 0.001), and inspiratory time (ß -0.7; 95% CI, -1.0 to -0.4; p < 0.001) were associated with resistive pressure. Multiple linear regression analysis showed the independent association between increasing respiratory system compliance, increasing airway resistance, increasing pressure above positive end-expiratory pressure, and decreasing inspiratory time and resistive pressure across all endotracheal tube sizes. Inspiratory time was the strongest variable associated with a proportional increase in resistive pressure. The contribution of airway resistance became more prominent with increasing endotracheal tube size. CONCLUSIONS: Peak inspiratory pressures measured during pressure controlled ventilation overestimated plateau pressure irrespective of endotracheal tube size, especially with decreased inspiratory time or increased airway resistance.

Effects of inspiratory muscle training on postural stability, pulmonary function and functional capacity in children with cystic fibrosis: A randomised controlled trial.

BACKGROUND: Previous research has found conflictive results regarding the benefits of inspiratory muscle training (IMT) for cystic fibrosis (CF) patients. Also, involvement of postural stability is a rising concern in chronic lung diseases but its role in CF patients is poorly understood. Our aim was to investigate the effects of IMT in CF patients as well as analysing the factors which may be related to postural stability. METHODS: Thirty-six children aged between 8 and 18 years with CF were randomly allocated to either "comprehensive chest PT" group (PT) or "IMT alongside comprehensive chest PT" group (PT+IMT). Both groups trained for 8 weeks. Dynamic and static postural stability tests on Biodex Balance system®, spirometry, respiratory muscle strength and 6-min walk distance (6MWD) was assessed at baseline and after 8 weeks of training. Determinants of postural stability was also analysed on baseline values. RESULTS: Maximum expiratory pressure (MEP) was found to be an independent predictor for overall limits of stability (LOS) score explaining %26 of variance (R = 0.514, p = 0.003). Overall LOS score, FVC, FEV1, peak expiratory flow, MEP and 6MWD significantly improved in both groups, with no significant differences between groups. Maximum inspiratory pressure (MIP) also improved in both groups but the magnitude of improvement in MIP was greater in PT+IMT group (38 cmH2O vs 13 cmH2O; p < 0.001). CONCLUSIONS: Combining IMT with chest PT failed to provide further improvements, except for MIP, suggesting that a comprehensive chest PT program may be individually effective in improving overall LOS score, spirometry, respiratory muscle strength and 6MWD. TRIAL REGISTRATION: www.ClinicalTrials.gov; registration number: NCT03375684.

Higher serum levels of systemic inflammatory markers are linked to greater inspiratory muscle dysfunction in COPD.

BACKGROUND: Chronic obstructive pulmonary disease (COPD) is associated with an inflammatory response that becomes more pronounced in acute exacerbations. Considerable attention has recently focused on the value of several inflammatory mediators in predicting worsening of COPD-related symptoms. Whereas respiratory muscle dysfunction is also widely present in this population, little is known about how systemic inflammation relates to inspiratory muscle dysfunction in COPD. METHODS: Fifty-three males with mild-to-very severe airflow obstruction underwent blood sampling for 23 inflammatory markers, including acute-phase proteins, cytokines and adipokines. Inspiratory muscle performance was assessed via the test of incremental respiratory endurance, providing measures of maximal (MIP) and sustained maximal (SMIP) inspiratory pressures. RESULTS: The mean ± SD MIP and SMIP were 75.32 ± 19.62 cmH2 O and 406.15 ± 124.55 PTU. MIP negatively correlated with CRP, SAA and cystatin C (r-values from -0.333 to -0.378, P < 0.02), while SMIP was inversely related to SAA and cystatin C (r = -0.534 and r = -0.396, P = 0.00). Significant differences in CRP, SAA, cystatin C and PARC were also found between subjects with and without inspiratory muscle weakness. No additional significant relationships were observed between either MIP or SMIP and other inflammatory markers in the study. CONCLUSIONS: MIP and SMIP are markedly reduced with greater degrees of inflammation in COPD as expressed by higher levels of CRP, SAA and cystatin C. Future research is needed to further examine the above findings and determine the impact of systemic inflammation along with its underlying mechanisms on inspiratory muscle function in COPD.

Beyond inspiratory muscle strength: Clinical utility of single-breath work capacity assessment in veterans with COPD.

BACKGROUND: Inspiratory muscle function in COPD has been traditionally described in terms of maximal inspiratory pressure (MIP). Arguably, however, is the day-to-day relevance of MIP, given that individuals rarely need maximal inspiratory forces to perform general tasks, but rather repeated breathing muscle contractions which demand endurance. The sustained maximal inspiratory pressure (SMIP) reflects the ability of the respiratory muscles to maintain force over time (i.e. single-breath work capacity). We investigated the relationships between SMIP and COPD-related clinical outcomes, hypothesizing that SMIP would have superior correlational and discriminatory value when compared to MIP. METHODS: 61 males with mild-to-very severe airflow obstruction underwent measures of spirometry, whole-body plethysmography, symptomatology, comorbidity, quality of life, exacerbations and mental health. MIP and SMIP were obtained via the Test of Incremental Respiratory Endurance. RESULTS: The mean ±â€¯SD MIP and SMIP were 77.2 ±â€¯22.9 cmH2O and 407.9 ±â€¯122.8 PTU. Both MIP and SMIP positively correlated with pulmonary function, with SMIP displaying the highest correlations. We found significant differences in spirometry, hyperinflation, symptomatology, exacerbation frequency, comorbidity, quality of life and anxiety in subjects grouped as having reduced or normal single-breath work capacity. Finally, significantly lower SMIP values were found in individuals with an IC/TLC ratio ≤25%. CONCLUSIONS: The assessment of SMIP appears to have superior clinical value than MIP in COPD. Our analyses revealed that subjects whose SMIP was reduced experienced more severe airflow obstruction, greater hyperinflation, as well as worse health and mental status with increased symptomatology and impaired quality of life.

A Rapid, Handheld Device to Assess Respiratory Resistance: Clinical and Normative Evidence.

INTRODUCTION: Following reports of respiratory symptoms among service members returning from deployment to South West Asia (SWA), an expert panel recommended pre-deployment spirometry be used to assess disease burden. Unfortunately, testing with spirometry is high cost and time-consuming. The airflow perturbation device (APD) is a handheld monitor that rapidly measures respiratory resistance (APD-Rr) and has promising but limited clinical data. Its speed and portability make it ideally suited for large volume pre-deployment screening. We conducted a pilot study to assess APD performance characteristics and develop normative values. MATERIALS AND METHODS: We prospectively enrolled subjects and derived reference equations for the APD from those without respiratory symptoms, pulmonary disease, or tobacco exposure. APD testing was conducted by medical technicians who received a 10-min in-service on its use. A subset of subjects performed spirometry and impulse oscillometry (iOS), administered by trained respiratory therapists. APD measures were compared with spirometry and iOS. RESULTS: The total study population included 199 subjects (55.8% males, body mass index 27.7 ± 6.0 kg/m2, age 49.9 ± 18.7 yr). Across the three APD trials, mean inspiratory (APD-Ri), expiratory (APD-Re), and average (APD-Ravg) resistances were 3.30 ± 1.0, 3.69 ± 1.2, and 3.50 ± 1.1 cm H2O/L/s. Reference equations were derived from 142 clinically normal volunteers. Height, weight, and body mass index were independently associated with APD-Ri, APD-Re, and APD-Ravg and were combined with age and gender in linear regression models. APD-Ri, APD-Re, and APD-Ravg were significantly inversely correlated with FEV1 (r = -0.39 to -0.42), FVC (r = -0.37 to -0.40), and FEF25-75 (r = -0.31 to -0.35) and positively correlated with R5 (r = 0.61-0.62), R20 (r = 0.50-0.52), X5 (r = -0.57 to -0.59), and FRES (r = 0.42-0.43). Bland-Altman plots showed that the APD-Rr closely approximates iOS when resistance is normal. CONCLUSION: Rapid testing was achieved with minimal training required, and reference equations were constructed. APD-Rr correlated moderately with iOS and weakly with spirometry. More testing is required to determine whether the APD has value for pre- and post-deployment respiratory assessment.

Predicting Survival After Extracorporeal Membrane Oxygenation for ARDS: An External Validation of RESP and PRESERVE Scores.

BACKGROUND: We aimed to test the performance of PRESERVE and RESP scores to predict death in patients with severe ARDS receiving extracorporeal membrane oxygenation (ECMO) with different case mixes. METHODS: All consecutive patients treated with ECMO for refractory ARDS, regardless of cause, in the Caen University Hospital in northwestern France over the last decade were included in a retrospective cohort study. The receiver operating characteristic curves of each score were plotted, and the area under the curve was computed to assess their performance in predicting mortality (c-index). RESULTS: Forty-one subjects were included. Pre-ECMO ventilator settings were: mean VT, 6.1 ± 0.9 mL/kg; breathing frequency, 32 ± 4 breaths/min; PEEP, 11 ± 4 cm H2O; peak inspiratory pressure, 48 ± 9 cm H2O; plateau pressure, 30.4 ± 4.4 cm H2O. At ECMO initiation, blood gas results were: pH 7.22 ± 0.17, PaO2 /FIO2 = 63 ± 22 mm Hg; PaCO2 = 56 ± 18 mm Hg; FIO2 = 99 ± 2%. Pre-ECMO data were available in 35 and 27 subjects for calculation of the PRESERVE score and RESP score, respectively. Pre-ECMO scoring system results were: median PRESERVE score, 4 (interquartile range 2-5), and median RESP score, 0 (interquartile range -2 to 2). Twenty-three subjects (56%) died, including 19 receiving ECMO. In univariate analysis, plateau pressure (P = .031), driving pressure (P = <.001), and compliance (P = .02) recorded at the time of ECMO initiation as well as the PRESERVE score (P = .032) were significantly associated with mortality. With a c-index of 0.69 (95% CI 0.53-0.87), the PRESERVE score had better discrimination than the RESP score (c-index of 0.60 [95% CI 0.41-0.78]) for predicting mortality. CONCLUSIONS: The use of these scores in helping physicians to determine the patients with ARDS most likely to benefit from ECMO should be limited in clinical practice because of their relatively poor performance in predicting death in subjects with severe ARDS receiving ECMO support. Before widespread use is initiated, these scoring systems should be tested in large prospective studies of subjects with severe ARDS undergoing ECMO treatment.

The Ratio of Inspiratory Pressure Over Electrical Activity of the Diaphragm Remains Stable During ICU Stay and is not Related to Clinical Outcome.

BACKGROUND: We previously described an index, defined as the ratio between the inspiratory muscle pressure (Pmus) and the electrical activity of the diaphragm (EA(di)) (Pmus/EA(di) index). In the present work, we describe the trend of Pmus/EA(di) index over time, investigating whether it could be an indicator of muscular efficiency associated with risk factors for diaphragmatic injury and/or clinical outcomes. METHODS: This work is a retrospective analysis of subjects with measurements of Pmus/EA(di) index obtained, on different days, during assisted ventilation. Effects of Pmus/EA(di) index absolute value on clinical outcomes were investigated dividing subjects into those with Pmus/EA(di) index higher or lower than the median. Effects of Pmus/EA(di) index trend over time were analyzed, distinguishing between subjects with Pmus/EA(di) index increasing or decreasing. RESULTS: Mean Pmus/EA(di) index was 1.04 ± 0.67, and the median (interquartile range) was 1.00 (0.59-1.34), without a systematic trend over the days. Demographic, ventilator, or outcome data did not significantly differ between subjects with Pmus/EA(di) index higher or lower than the median. Similarly, we did not find relevant differences in subjects with Pmus/EA(di) index increasing or decreasing over time. CONCLUSIONS: The Pmus/EA(di) index value remained constant in each subject over time, although the inter-individual variability was high. Neither the Pmus/EA(di) index nor its trends appeared to be associated with ventilatory variables or clinical outcome.

Maximum Inspiratory Pressure is a Discriminator of Pneumonia in Individuals With Spinal-Cord Injury.

BACKGROUND: Respiratory complications remain a major cause of mortality among individuals with spinal-cord injury (SCI). The present study investigated whether respiratory function is a discriminator of pneumonia in individuals with SCI and is aimed to determine the best predictive parameter. METHODS: This was a retrospective cohort study. Individuals with traumatic SCI, level C3 to T12, complete and incomplete lesions, were included. Data on respiratory function were extracted from medical records. The receiver operating characteristic curve was calculated for each parameter (forced vital capacity, FEV1, peak expiratory flow, and maximum inspiratory and expiratory pressure [PImax and PEmax]) to determine the discriminator with the largest area under the curve between individuals with and without pneumonia. RESULTS: Data of 307 subjects were analyzed. PImax was identified as the best discriminator between individuals with and without pneumonia, both in motor complete (area under the curve 0.86, 95% CI 0.78-0.93, P < .001) and incomplete individuals (area under the curve 1.0, 95% CI 1.00-1.00, P < .001). In individuals with motor complete lesions, the threshold value for PImax was 115% of the lesion-specific reference value (sensitivity 74.4%, specificity 83.4%). In motor incomplete individuals, the PImax threshold value was 93.5 cm H2O (sensitivity 100%, specificity 100%). CONCLUSIONS: PImax is the best discriminator between spinal cord-injured individuals with versus those without pneumonia. Individuals with a PImax below threshold values are at risk of pneumonia.